1. Field of the Invention
This invention relates to metal window and/or door frames, and particularly to a frame incorporating a thermal break disposed between the inner and outer parts of a frame.
2. Description of the Prior Art
Metal extrusions, particularly aluminum extrusions, are widely used in the construction of door and/or window frames, because of the advantages afforded by the strength, ease of maintenance etc. of the finished construction. However, the thermal properties of the metal tend to result in the formation of condensation when one part of the frame is subjected to lower temperatures than are experienced by another part of the frame, e.g. by the side of a door frame exposed to the exterior of a building which tends to be colder than the inner side exposed to the building interior. To combat this, a thermal break is provided between the two parts of the frame, being in the form of a layer of thermal barrier material, usually a rigid resin, which connects the two parts of the frame so that there is no direct metal-to-metal contact between them.
One widely used method of constructing a thermal break is illustrated in FIGS. 1 and 2 of the accompanying drawings, and involves the use of a one-piece aluminium extrusion which comprises the outer element 1 of the frame and the inner element 2 of the frame, the elements 1 and 2 having respective confronting surfaces 3 and 4 which are spaced apart by a thin web 5 which at this stage connects the elements 1 and 2. In other words, there is formed between the elements 1 and 2 a shaped channel of which the walls are defined by the confronting surfaces 3 and 4, and the web 5. The shaped channel is then filled with a resin material, and when this has cured and thus rigidified, the base of the channel constituted by the web 5 is removed by a machining operation to leave the construction shown in FIG. 2 where the resin material 6 constitutes the sole connection between the parts 1 and 2. Conveniently the surfaces 3 and 4 are undercut as shown at 7, to provide a secure connection between the resin material 6 and the elements 1 and 2.
Although the method described above is suitable to produce a construction such as that shown in FIG. 2, there is a need for a box-like construction such as that shown in FIG. 3 of the accompanying drawings, where the elements 1 and 2 are connected by a thermal break comprising two parallel strips of resin 6 and 6A, disposed in opposite side walls of a box-like section. Frequently this box-like construction is required in lengths of up to 5 meters, and it will be readily appreciated therefore that if the method described with reference to FIGS. 1 and 2 is applied to the box-like construction, the appearance of the construction after the formation of the thermal breaks 6 and 6A would be as is shown in FIG. 4 of the accompanying drawings, requiring a difficult if not impossible machining operation to remove the unwanted webs 5 and 5A inside the box section.
The object of the present invention is to provide a method of forming a thermal break which does not require the subsequent removal of unwanted metal webs, and apparatus for performing this method, which is therefore particularly suitable for the production of the box-like construction shown in FIG. 3 of the accompanying drawings.